Method of making an aluminum clad steel wire



United States Patent 3,306,088 METHOD OF MAKING AN ALUMINUM CLAD STEELWIRE Orville E. Adler, Niles, Mich, assignor to National-StandardCompany, a corporation of Delaware No Drawing, Application Feb. 14,1963, Ser. No. 258,- 635, which is a continuation of application Ser.No. 19,488, Apr. 14, 1960. Divided and this application Oct. 7, 1965,Ser. No. 493,891

8 Claims. (Cl. 72-47) The present application relates to a method ofmaking an aluminum clad steel wire which is especially suitable for useas an electrical conductor wire; and is a division of my copendingapplication Serial No. 258,635, filed February 14, 1963, which in turnis a continuation of my copending application Serial No. 19,488, filedApril 4, 1960, and now abandoned.

There are many places where aluminum coated steels could be used; butthe methods heretofore available for producing such steel have greatlylimited the use of the articles, because the only method for rapidlycoating steel with aluminum has been a hot dip method. A properlycleaned steel surface may be contacted with molten aluminum in thepresence of a suitable flux to form an aluminum-iron alloy which bondsthe aluminum to the steel. This alloy is quite brittle, so that theresulting aluminum coated article is useful only in applications whichrequire little or no deflection of the material. Furthermore, thethickness of coating which may be applied to a steel base in this manneris very limited, which again places a limitation on the area ofusefulness of the resulting coated material. It has practically beenunavailable as an electrical conductor because the aluminum-iron alloyis a very poor conductor of electricity, and because of the thinaluminum coating.

As far back as 1907 it was suggested in Patent 867,658 that an electricconductor wire be manufactured by extruding aluminum around a steelcore. In spite of the obvious advantages of such a material, due to thehigh electric conductivity of aluminum, nobody has successfullymanufactured it in commercial quantities. The fact is that what wasthought in 1907 to be a simple method to carry out has proved to beextremely difiicult, due to the problem of obtaining a satisfactory bondbetween the aluminum and the steel core. By a proper correlation betweentemperature, pressure and rate of wire travel through the extruding dieit is possible to obtain a satisfactory bond; but it has not beenpossible to do so at high enough speed to make the process commerciallypractical.

I have now discovered that the rate at which aluminum may be extrudedonto a steel core wire may be enormously increased if the core wire isfirst plated with copper or nickel, and the plated surface is thoroughlyclean when the aluminum is extruded onto it. The copper or nickel plateis deposited upon the steel core by electroplating.

Either copper or nickel must be thoroughly cleaned before the aluminumextrusion takes place, and such cleaning may be by any of the acceptedmethods, either chemical or abrasive cleaning. In the case of copper, itis important that the cleaned plated wire be passed immediately throughthe aluminum extruding die, or that it be carried in an inertatmosphere, because of the rapidity with which clean copper corrodes.The greater corrosion resistance of nickel makes such care unnecessary.

Any wire which is to be used in large quantities as a conductor must becapable of being drawn without failure of the bond between the aluminumand the steel; and the wire produced by the present method is entirelyadequate from this standpoint, since it can be drawn by conventionalmethods to produce any needed size reduction.

The aluminum sheath is amply ductile for the intended purpose, asevidenced by the fact that the wire may be wrapped around its owndiameter without showing any flaking, cracking or separation.

As an example of a commercially usable electric condnctor wire, thesteel core is a .125" carbon steel and the thickness of the copper ornickel coating is .0004". The aluminum sheath has a thickness of .013".Such a wire, if sheathed with substantially pure aluminum, theconductivity of which is 65 has a conductivity of 30% taking pure copperas Such conductivity is determined with direct current, or withalternating current not greatly in excess of 60 cycles, and would difierat higher frequencies. The wire may be drawn to .064" by conventionalwire drawing methods without any failure of the bond, and may be wrappedaround its own diameter without any flaking, cracking or separation ofthe coating. After drawing, the .064" wife has a breaking strength of526 lbs.

Such aluminum clad steel may be used where strength, conductivity,lightweight, or corrosion resistance is a desirable characteristic. Analuminum coated steel wire of 30% conductivity weighs only 70% as muchas does an equivalent conductor of copper coated steel. However, it hasa somewhat lower tensile strengthfbecause the conductivity per unitvolume of aluminum is only 65% that of copper, so that for a givenoutside diameter of the conductor wire the steel core must be relativelysmaller in order to raise the conductivity to the desired level.Likewise, the tensile strength of aluminum is less than that of copperwhich contributes to the over all reduction in tensile strength of thewire.

On the other hand, by increasing the outside diameter of the aluminumclad Wire from .064" to .067" and using the same tensil strength steelcore as on the .064 copper clad steel, a wire is produced which has abreaking strength and electrical resistance equal to that of the copperclad wire, and which still Weighs only 83.2% as much as does the copperclad conductor.

It is obvious that the weight of the conductor is very important inelectrical transmission lines and communication lines, because theself-weight of the wire determines the distance between poles, the iceand wind load which the wires will tolerate, and sag and tensionrequirements. Likewise, aluminum clad conductors are less expensive thancopper clad, both because of the favorable conductivity-weight ratio andbecause of the lower cost of aluminum as compared to copper.

As an example of the method used to produce the foregoing wire, a .125"carbon steel wire is cleaned and copper or nickel plated in anyconventional manner. The wire is then cleaned, and it is important thatthe aluminum be extruded onto the surface while it is clean. The desiredsurface may be readily obtained by a bufiing, or abrasive cleaningmethod, since such a surface does not tarnish readily. Common chemicalcleaning procedures may be used, although if such procedures are used oncopper the wire must be kept in an inert atmosphere from the cleaningtank to the extruding die.

For an example of a preferred extruding press and die for practicing thepresent method, reference is made to the copending application ofWilliam F. Hope, Serial No. 165,815, now Patent No. 3,112,148, filedJanuary 2, 1962, as a continuation of abandoned application Serial No.23,219, filed April 19, 1960. The Wire is passed through the extrudingdie, preferably by pulling, and an aluminum slug, or billet in the dieis heated to a temperature of about 1000 F. and is extrudedconcentrically onto the copper plated wire core under a pressure of atleast 50,000 lbs. per square inch on the slug.

Since a substantial part of the total extruding pressure is requiredmerely to overcome resistance in the die, it is obvious that pressure onthe plated core is substantially less than 50,000 p.s.i. Furthermore, itis clear that with a press and die design requiring less force merely toovercome resistance, an adequate bond may be obtained at a lowerpressure on the slug than that above stated.

The copper plating of the steel core has permitted extrusion speeds upto 28 feet per minute, at the above pressure, in the particular pressand die above referred to, whereas without the copper layer an extrusionspeed in excess of feet per minute failed to produce a satisfactory bondbetween the aluminum and the core wire. With a press which will take aslug of more than 1 /8" diameter, it is clear that faster extrusionshould be possible at the same pressure on the slug.

It is possible to produce a satisfactory bond without a freshly cleanedcopper surface if the extrusion pressures are substantially increased.Operating at the same temperature in the above mentioned press and die,an extrusion pressure of 70,000 psi. on the aluminum slug has produced asatisfactory bond even upon a tarnished copper or nickel surface.

The excellent bond obtained between the aluminum and the copper ornickel plated wire is believed to be due, at least in part, to arecrystallization of the copper or nickel at the temperature andpressure of the extrusion operation. The copper or nickel layer alsoprevents alloying of the aluminum and steel core if the wire is annealedduring processing. Further, since neither the copper nor the nickel northe extruded aluminum is in a molten state there is no alloying of thealuminum with the thin layer beneath it, or with the ferrous base; andthis is very advantageous because such alloys are very brittle andprovide a fragile bond between the various layers in the wire, as wellas reducing the electric conductivity of the aluminum.

At the processing temperature herein disclosed, a strong bond isobtained upon a core which is not cold worked after plating. It is knownthat cold working decreases the recrystallization temperature of copper,and accordingly the aluminum may be extruded onto a copper plated wireat considerably lower temperatures if the copper is first cold worked.

The above method may be followed if nickel is used instead of copper,except that cleaning of the nickel surface is not as important becauseit does not corrode as easily as copper.

A wire in accordance with the present invention may be drawn from .151"to .064" in seven passes, either with or without annealing betweenpasses. Any standard lubricant used for drawing aluminum issatisfactory, a preferred lubricant being a mixture of 95 parts of SAE10 motor oil and 5 parts of tallow.

The composite wire after being drawn to any desired size smaller than.151 has the characteristic elongated grain structure of drawn metal, inthe ferrous metal core and also in the aluminum sheath. This differsfrom the substantially equi-axial grain structure of an undrawnmaterial.

It has been proposed in the prior art to form a composite metal slug bydipping a ferrous billet first into a pot of heated copper, the billetbeing in a jacket with a removable bottom which permits the billet to bewithdrawn with a layer of copper in the jacket, and permitting the layerto solidify on the billet; and thereafter repeating the operation so asto cast an aluminum sheath around the billet and copper.

There are several reasons that the foregoing process cannot produce asatisfactory continuous spool length of composite wire. In the firstplace, the minimum practical temperature for a molten aluminum bath fordepositing aluminum on a core is approximately 1300, and at thistemperature the aluminum and copper form a copperaluminum alloy, eventhough the copper melts at a much Percent Cu added: (Cu

In the second place, unless a very thick layer of copper is used, thecopper does not act as a barrier between the aluminum and the ferrousmetal core; and the interface between the aluminum and the ferrous coreconsists of a brittle layer containing aluminum, iron, and perhapscopper. The same is true if nickel is used instead of copper. Suchmaterial cannot be drawn by any known methods, because the bond betweenthe aluminum and ferrous core fails upon drawing.

In the third place, it is quite obvious that casting a sheath around abillet produces an article which must be reduced by rolling, and couldnot possibly be drawn. Even if the ferrous metal core were of smallenough diameter to permit drawing, it is apparent that the maximumlength to which the composite metal slug might be drawn (even if capableof being drawn), would be only a few feet.

Thus, in no case does the foregoing process produce a composite articlehaving a discrete layer of copper or nickel on a ferrous core, and analuminum sheath which is substantially uncontaminated by copper ornickel and thus has substantially unimpaired electric conductivity.

In addition it is a well known fact that aluminum con taining copper hasconsiderably lower corrosion resistance than aluminum free from copper;and since corrosion resistance is very important for an electricalconductor wire, this provides a further reason that a process whichbrings copper into contact with molten aluminum is not a practical wayto produce an electrical conductor wire.

The foregoing detailed description is given for clearness ofunderstanding only and no unnecessary limitations are to be understoodtherefrom, as some modifications will be obvious to those skilled in theart.

I claim:

1. A method of making an aluminum clad ferrous metal wire comprising:plating the ferrous metal wire with a metal selected from the groupconsisting of copper and nickel; heating a slug of aluminum to atemperature of about 1000 F.; and extruding the heated aluminum ontosaid plated wire at a pressure of at least about 50,000 p.s.i. on theslug while the wire is moved endwise at a uniform speed.

2. A method of making an aluminum clad ferrous metal wire comprising:copper plating the ferrous metal wire; heating a slug of aluminum to atemperature of about 1000 F.; and extruding the heated aluminum ontosaid plated wire at a pressure of at least about 50,000 p.s.i. on theslug while the wire is moved endwise at a uniform speed.

3. A method of making an aluminum clad ferrous metal wire comprising:nickel plating the ferrous metal wire; heating a slug of aluminum to atemperature of about 1000 F.; and extruding the heated aluminum ontosaid plated wire at a pressure of at least about 50,000 psi. on the slugwhile the wire is moved endwise at a uniform speed.

4. A method of making an aluminum clad ferrous metal wire comprising:copper plating the ferrous metal wire; cleaning the plated wire toproduce a clean copper surface; heating a slug of aluminum to atemperature of about 1000 F.; and extruding the heated aluminum onto theclean copper surface at a pressure of at least about 50,000 p.s.i. onthe slug while the wire is moved endwise at a uniform speed.

5. A method of making an aluminum clad ferrous metal Wire comprising:copper plating the ferrous metal wire; abrasive cleaning the plated Wireto produce a clean copper surface; heating a slug of aluminum to a temperature of about 1000 F.; and extruding the heated aluminum onto saidclean surface at a pressure of at least about 50,000 p.s.i. on the slugwhile the wire is moved endwise at a uniform speed.

6. A method of making a drawn, aluminum clad ferrous metal wirecomprising: plating the ferrous metal Wire with a metal selected fromthe group consisting of copper and nickel; heating a slug of aluminum toa temperature of about 1000 F.; extruding the heated aluminum onto theplated Wire at a pressure of at least about 50,000 p.s.i. on the slugWhile the wire is moved endwise at a uniform speed; and drawing the Wireto reduce its diameter.

7. A method of making an aluminum clad ferrous metal wire comprising:plating the ferrous metal wire with a metal selected from the groupconsisting of copper and nickel; heating a slug of aluminum to therecrystallization temperature of the plated metal; and extruding the 6heated aluminum onto said plated wire at a pressure of at least about50,000 p.s.i. on the slug while the wire is moved endwise at a uniformspeed.

8. A method of making an aluminum clad ferrous metal wire comprising:copper plating the ferrous metal wire; heating a slug of aluminum to therecrystallization temperature of copper; and extruding the heatedaluminum onto said plated wire at a pressure of at least about 50,0000p.s.i. on the slug while the wire is moved endwise at a uniform speed.

References Cited by the Examiner UNITED STATES PATENTS 929,778 8/1909Monnot 29-197 2,391,752 12/1945 Stern 20710.2 2,670,309 2/1954McClintock 207l0.2 2,795,467 6/1957 Colwell 207-102 2,828,859 4/ 1958Emmerich 20710.2 2,830,643 4/1958 Harris 207-1.2 X 2,841,546 7/1958Robinson 20710.2

CHARLES W. LANHAM, Primary Examiner. A. L. HAVIS, Assistant Examiner.

1. A METHOD OF MAKING AN ALUMINUM CLAD FERROUS METAL WIRE COMPRISING:PLATING THE FERROUS METAL WIRE WITH A METAL SELECTED FROM THE GROUPCONSISING OF COPPER AND NICKEL; HEATING A SLUG OF ALUMINUM TO ATEMPERATURE OF ABOUT 1000*F.; AND EXTRUDING THE HEATED ALUMINUM ONTOSAID PLATED WIRE AT A PRESSURE OF AT LEAST ABOUT 50,000 P.S.I. ON THESLUG WHILE THE WIRE IS MOVED ENDWISE AT A UNIFORM SPEED.